Hot Docs unveiled its ‘biggest festival yet’ on Tuesday, as organizers pulled back the curtain on 170 documentaries from 36 countries that are set to unspool when the fest returns to Toronto in April.

‘We’re screening more films than we’ve done before, but we’ve added a lot of rigor,’ said director of programming Sean Farnel at a press conference.

The 15th edition of the fest will open April 17 with Anvil! The Story of Anvil, the directorial debut of Sacha Gervasi, a one-time roadie who followed the Canadian heavy-metal band around the world, looking at the hopes and dreams of its 50-something members Steve Kudlow and Robb Reiner.

The Canadian opener is Air India 182, written and directed by Sturla Gunnarsson (Beowulf & Grendel) about the 1985 terrorist attack that left 329 people dead. The picture will evoke a tremendous sense of sorrow, but also ‘hopes to provoke outrage,’ said Gunnarsson.

Planning for a spike in attendance, organizers have added two new venues, the Cumberland theater and the Winter Garden theater, for the opening.

‘I’m anticipating our strongest program,’ said executive director Chris McDonald. ‘We have all kinds of records for submissions and number of countries represented. It was only five or six years ago when we were screening in bars and cafes on College Street.’

A new program called Next will show work by and about artists, and Hot Docs will this year spotlight Iran and Mexico. Also new for industry delegates is a digital on-demand library of titles.

‘We’ve had it for several years where buyers were screening them on DVDs, but now it’s going to be an on-demand,’ said Brett Hendrie, managing director of Hot Docs.

All Together Now, a copro between Cirque du Soleil Images and Apple Records, will have its world premiere. A behind-the-scenes look at Cirque du Soleil’s show Love, which was itself inspired by the Fab Four, includes interviews with Ringo Starr and Paul McCartney. Director Adrian Wills said he ‘was able to get verité moments, including the Beatles watching the Cirque show.’

Also in the program is the White Pine Pictures/National Film Board copro Triage: Dr. James Orbinski’s Humanitarian Dilemma, in which the president of Doctors Without Borders returns to Somalia and Rwanda to deal with his past.

This year’s International Spectrum — a curated competition of 28 new documentaries — includes Min Sook Lee’s Tiger Spirit, a look at the division between Korea’ s north and south.

Hot Docs runs from April 17-27. Visit www.hotdocs.ca for more information.